The present invention relates to a drug delivery matrix coating, to an implantable device comprising the drug delivery matrix coating, to a method for making the drug delivery matrix coating and to a method for applying the drug delivery matrix coating to a stent.
Stents are typically implanted within a vessel in a contracted state and expanded when in place in the vessel in order to maintain patency of the vessel to allow fluid flow through the vessel. Typically, implantation of such stents is accomplished by mounting the stent on the balloon portion of a catheter, positioning the stent in a body lumen, and expanding the stent to an expanded state by inflation of a balloon within the stent. The stent can then be left in place by deflating the balloon and removing the catheter.
Because of the mechanical strength that is required to properly support vessel walls, stents are typically constructed of metallic materials. However, it is frequently desirable to provide localized pharmacological treatment of a vessel at the site being supported by the stent. It is convenient to employ the stent as a vehicle for drug delivery. The metallic materials are not capable of carrying and releasing drugs. Polymeric materials capable of absorbing and releasing drugs typically do not fulfill the structural and mechanical requirements of a stent, especially when the polymeric materials are loaded with a drug, since drug loading of a polymeric material diminishes the structural and mechanical properties of the polymeric material. Since it is often useful to provide localized therapeutic pharmacological treatment of a vessel at the location being treated with the stent, it is desirable to combine such polymeric materials with existing stent structures to provide a stent with the capability of absorbing therapeutic drugs or other agents, for placement and release of the therapeutic agents at a specific intravascular site.
One solution historically used has been coating a stent""s metallic structure with a polymeric material in order to provide a stent capable of both supporting adequate mechanical loads as well as delivering drugs. Techniques typically used to join polymers to metallic stents include dipping, spraying and conforming processes. However, these techniques have tended to introduce other problems into the stent products. Other problems with drug delivery matrix coatings include marginal adhesion to a substrate such as a metal substrate, insufficient elongation of the coating resulting in cracks, and limited and sub-optimal solvent choices that result in difficult application of the coating and poor manufacturability.
The present invention relates to a copolymer of carboxylic acid in a layer as applied in a drug releasing implant. The carboxylic acid copolymer may be in a matrix having a drug or in a primer or in a diffusion barrier.
One embodiment of the present invention includes a drug delivery coating. The drug delivery coating comprises a matrix comprising one or more co-polymers of ethylene comprising the reaction products of carboxylic acid containing unsaturated monomers. The drug delivery coating also includes a drug contacting the matrix. The drug delivery coating has a strong adhesion due to Van der Waals interaction resulting from carboxylic acid bonding of the coating to the material being coated.
One other embodiment of the present invention includes a stent. The stent comprises a tubular main body. The stent also comprises a coating that is adhered to the tubular main body. The coating comprises one or more co-polymers of ethylene wherein the co-polymers include a carboxylic acid moiety. The carboxylic acid moiety comprises one or more of acrylic acid, methacrylic acid, maleic acid, itaconic acid and all combinations and esters of these monomers. The coating deforms to a degree that accommodates stent deformation and, as a result, is resistant to cracking and delamination. The coating adheres to stents comprised of materials such as stainless steel.
Another embodiment of the present invention includes a drug delivery system. The drug delivery system comprises a tubular main body and a first coating that overlays the tubular main body. A drug is incorporated into the first coating. A coating comprising one or more co-polymers of ethylene with a carboxylic acid moiety overlays the first coating. The carboxylic acid moiety is one or more of acrylic acid, methacrylic acid, maleic acid, itaconic acid and all combinations and esters of these monomers. For some embodiments, the first coating is biodegradable.
Another embodiment of the present invention includes a method for improving manufacturability of a drug delivery system used with a medical device. The method comprises providing a medical device with a main body and providing a coating comprising cross-linkable co-polymers of ethylene with carboxylic acid. The method also includes applying the coating to the main body of the medical device.
The drug delivery coating of the present invention adheres to a metal substrate and has an elongation comparable to a metal or polymeric substrate. The drug delivery coating is soluble in a ternary blend. The ternary blend eases application of the coating to a medical device surface, such as a stent. The ternary blend also improves manufacturability as compared to polymeric drug delivery systems not using the ternary blend.